1. Field of the Invention
The present invention generally relates to a manufacture method of a thin film transistor substrate, the thin film transistor substrate and a thin film transistor liquid crystal display.
2. Description of Prior Art
A large size TFT-LCD (Thin Film Transistor Liquid Crystal Display) has been widely used in the flat panel TV field. What is most significant and different from PC monitor and mobile phone screen, the wider view angle is much more required. Therefore, people can watch the TV images more clearly from any angles.
As regarding of VA (Vertical Alignment) panel, a traditional method of increasing the view angle is to divide one pixel into two sub pixels. Each sub pixel is arranged as 4 domain structure due to the different ITO directions of the pixel electrodes. The pixel electrode of one sub pixel is coupled to the charge-sharing common capacitor through a TFT switch. When the TFT switch is on, the charge of the sub pixel will partially flows to the charge-sharing common capacitor and leads to that the voltage of this sub pixel is slightly smaller than the voltage of the other sub pixel. Consequently, the brightnesses of these two sub pixels become different. Then, 8 domain structure can be obtained to increase the view angle of the images.
In general, the signal line metal electrode and the metal gate electrode are employed as capacitor electrode plates of the charge-sharing common capacitor. An isolation layer sandwiching an As layer is formed as a MIM (Metal injection Molding) structure. In the five-mask process, the active amorphous silicon layer and the active ohmic contact layer (P-doped silicon layer) of the As layer are both etched. Therefore, the only the silicon nitride isolation layer is sandwiched by the two metal electrode plates of the charge-sharing common capacitor. The capacitance of such capacitor does not vary when the positive and negative polarities of the metal plates are changed.
However, for magnifying productivity of TFT-LCD substrates to reduce the production cost, the five-mask process has been improved as four-mask process, i.e. the photolithography process and etching process are canceled and the formation of the second metal electrode layer is directly implemented after the gate electrode isolation layer and the active layer are formed by CVD (chemical vapor deposition). Then, with a half tone mask going with wet etching and dry etching processes, the signal electrode and TFT trench are formed. In the charge-sharing common capacitor of the four-mask process, a complete CVD film is sandwiched by the signal line metal electrode and the metal gate electrode. The CVD film comprises an isolation layer, an amorphous silicon layer and an ohmic contact layer. When the amorphous silicon layer, the ohmic contact layer and the isolation layer are sandwiched, the only distinction is the condition of the silicon nitride isolation layer. When the capacitance varies as positive and negative polarities of the two metal electrode plates are changed. The video quality and reliability descending due to the abnormalities of afterimages, flickers and et cetera, which are caused by capacitance variation.